feat(i18n): full RTL/CJK support — fonts, Japanese locale, directional fixes

Bundle Noto Sans Arabic + Noto Sans JP (SIL OFL 1.1) as per-glyph fallbacks
for both the UI text theme and every generated PDF, so RTL (Arabic) and CJK
render on all platforms — including desktop, where the system font may lack
them — instead of tofu. A shared pdf_fonts.dart centralizes the PDF theme and
the three label/catalog/recovery services reuse it.

Add Japanese (ja) as the CJK reference locale — fittingly, the app's own name
is Japanese (種, tane, 'seed'). Core strings translated; the rest fall back to
English via slang. Wired into supportedLocales (automatic) and the settings
picker.

Fix three physical Alignment.centerLeft -> AlignmentDirectional.centerStart in
variety_detail_screen, and make month-abbreviation and avatar-initial
truncation grapheme-safe (.characters) so CJK text is never cut mid-character.

Tests: CJK/Arabic PDF glyph render, ja locale resolution + English fallback.
The chat-bubble mirroring flagged by the audit was verified correct (already
respects Directionality) and left unchanged.

docs/i18n.md

@@ -10,11 +10,15 @@ speaks nested JSON) handles natively.
 ```
 apps/app_seeds/lib/i18n/
   en.i18n.json   ← base locale (source of truth for keys)
-  es.i18n.json
-  pt.i18n.json
+  es.i18n.json   ast, pt, fr, de, ja …
   strings*.g.dart  ← generated, do not edit
 ```
 
+Live locales: `es`, `ast`, `en`, `pt`, `fr`, `de`, `ja`. Japanese (`ja`) is the
+CJK reference — fittingly, the app's own name is Japanese (種, *tane*, "seed").
+It ships only a core set of strings translated; the rest fall back to English,
+which is exactly how a partial locale is meant to grow.
+
 - Placeholders use braces: `"{count} entries added"`. Keep them verbatim.
 - Keys are code and never change per locale; only values are translated.
 - Missing keys fall back to English at runtime (`fallback_strategy:
@@ -41,6 +45,16 @@ apps/app_seeds/lib/i18n/
 Right-to-left locales (Arabic, Hebrew, Persian) are first-class: layouts use
 directional insets and are exercised by
 [`rtl_smoke_test.dart`](../apps/app_seeds/test/ui/rtl_smoke_test.dart).
+
+**Fonts cover the scripts we claim.** The UI text theme carries Noto Sans
+Arabic + Noto Sans JP as per-glyph fallbacks (see
+[`theme.dart`](../apps/app_seeds/lib/ui/theme.dart)), so RTL and CJK render on
+every platform — including desktop, where the system font may lack them. Every
+generated PDF shares the same fallbacks via
+[`pdf_fonts.dart`](../apps/app_seeds/lib/services/pdf_fonts.dart), so labels and
+catalogs print Arabic/CJK instead of tofu. Fonts are a per-locale resource,
+extensible to any script; widen the fallback list as more scripts land.
+
 Locale-specific resources ship with their locale, never hardcoded: OCR
 language packs (`assets/tessdata/`), PDF fonts (`assets/fonts/`), and species
 common names (`assets/catalog/species.json`, a locale-keyed map).